© 1993KluwerAcademicPublishers. Printedin the Netherlands.
Kinetics of growth and sugar consumption in yeasts
J ohannes R van Dijken, Ruud A. Weusthuis & Jack T. Pronk
D epartment of Microbiology and Enzymology, Kluyver Laboratory of Biotechnology, Julianalaan 67, 2628 BC Delft, The Netherlands
K ey words: a lcoholic fermentation, chemostat culture, Crabtree effect, respiration, Saccharornyces cerevisiae, y easts
A n overview is presented of the steady- and transient state kinetics of growth and formation of metabolic b yproducts in yeasts. Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even u nder fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This s o-called 'Crabtree effect' probably results from a multiplicity of factors, including the mode of sugar transp ort and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree e ffect in S. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, v ery high respiration rates can be achieved by this yeast. S. cerevisiae is an exceptional yeast since, in contrast t o most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic c onditions.
' Non-Saccharomyces' y easts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth condit ions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth a nd therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right o xygen dosage in large-scale fermentations, non-Saccharornyces y easts are therefore not suitable for larges cale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also d ependent on the type of sugar. For example, the facultatively fermentative yeast Candida utilis d oes not f erment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid o xidative growth.
T he yeast collection of the Centraal Bureau voor
S chimmelcultures (CBS, Delft, The Netherlands)
h arbours all (over 4,500) natural yeast isolates des cribed in the literature. These belong to 640 species t hat have been grouped into 75 genera. Due to its
' classical' industrial applications in the rising of
d ough and in beer and wine fermentation, Sacchar omyces cerevisiae is the best-known representative o f this group of microbes. In fact, 'yeast' and S. cerevisiae a re frequently used as synonymous terms.
H owever, S. cerevisiae is a rather exceptional yeast
s ince it is one of the few yeasts that are able to grow
a naerobically (Visser et al. 1990). Also during aerob ic growth, this yeast shows an unusual behaviour. W hen grown aerobically at a low rate, under sugar
l imitation, cultures tend to spontaneously synchron ize their cell cycle (von Meyenburg 1969; Parulek ar et al. 1986), which makes the analysis of chemical kinetics of growth a difficult enterprise. I n the past decade, yeasts other than S. cerevisiae
h ave gained industrial interest as hosts for the exp ression of heterologous genes. Examples are
m ethanol-utilizing yeasts such as Hansenula polymorpha a nd Pichiapastoris a nd the lactose-utilizing s pecies Kluyveromyces lactis a nd K. marxianus
( Romanos et al. 1992). Several arguments have
b een put forward to use 'non-Saccharomyces
y easts' as hosts for heterologous gene expression,
i ncluding broader substrate specificity, availability
o f strong inducible promoters, absence of aerobic
a lcoholic fermentation (i.e. absence of the Crabtree
e ffect), etc. However, a major factor, decisive for
t he use of alternative...